I remembered associating burst radius with the terms linearly and 20%, but a quick search didn't help so I took a guess and assumed it dropped linearly to 50%. It's interesting and makes sense that it deals full damage at half radius. I also learned that hydro and chute vent last for 3 seconds not 5 like I've always claimed.
As for angles against hwatchas, there aren't many options. Heavy clip hwatcha is generally not a problem except against heavy guns/engines, the main issue is mid-close burst. There are 3 options: stay out of effective range, stay above arcs, or stay below. Tactics differ whether your ship relies on maneuverability or firepower. If you use tools/stamina/buffs well you can dodge a hwatcha volley but sometimes this isn't an option. If you get hit a good tactic is waiting to rebuild until next volley because it's unlikely that you can rebuild and shoot effectively before the hwatcha finishes reloading.
For squid against fish you have 2 options: avoid the shot or start low. Burn in, give them an easy shot, and dodge. That'll buy time while they reload. It's safest to avoid arcs altogether but this limits options of how to engage. The other option is staying low and draw them downwards then hydro up. They'll have downward momentum and you'll shoot upwards. Quickly get as close as possible.